Genetics Flashcards
16 weeks pregnant female. She asks you if this baby will also have spina bifida like her daughter as it is also a girl. They live in Grassy Park. She has seen a genetics doctor who told her, her daughter has “non-syndromic spina bifida”. She also asks what tests are available to look for spina bifida in a pregnancy.
Describe what you would tell her (5)
Recurrence risk for isolated neural tube defects in the Western Cape is around 5%. It can be reduced with folic acid supplementation taken periconception. The gender is irrelevant.
Tests available: maternal serum AFP screening/ High resolution ultrasound/ MRI/ occasionally amniocentesis for AFP in selected cases only – not routinely!
List three (3) factors that could increase the risk that this foetus would have spina bifida (1½)
Maternal drugs such as anti-eplileptics or MTX, excessive alcohol intake, malnutrition, maternal diabetes
The fetus turns out to be anecephalic. State the likely inheritance pattern in this family (½)
Multifactorial inheritance
Miss Green is 42 years old and discovers that she may be pregnant as she had missed her last period. She is devastated as she is an unmarried CEO at a large company with a very demanding career and was not prepared to have children. She becomes depressed and considers having an abortion as the father is her recently married 22-year-old intern. In much emotional turmoil she visits her GP who happens to be a staunch Catholic and convinces her against having an abortion. Miss Green reluctantly continues through her pregnancy with worsening depression until a routine antenatal ultrasound scan shows a large fetal spinal defect. The gynaecologist doing the scan counsels Miss Green on the implications and further testing as well as her option of termination of pregnancy (TOP).
There are additional anomalies found on the scan including clenched hands and a heart defect.
List four (4) possible causes for NTD with these additional abnormalities (½x4 = 2)
Chromosome abnormalities e.g. trisomy 18
Maternal diabetes
Anticonvulsant embryopathy
Alcohol teratogenicity
Single gene disorders e.g. Meckel Gruber Syndrome (either answer accepted for a mark)
State what you think the most likely diagnosis is in light of her age (½)
Trisomy 18
State whether Ms Green would be offered a TOP at 22 weeks of gestation and give a reason (1½)
Yes, severe fetal abnormality
List four (4) psychosocial factors that may influence Ms Green’s handling of the situation that you should consider when counselling her (½x4 = 2)
Age, Parity, Social/ cultural background, Religion, Support, Financial, Previous experiences with disability
Mrs Abrahams is 46 years old when she becomes pregnant with her 3rd child. On routine antenatal ultrasound the doctor suspects that the fetus may have a neural tube defect. Mrs Abrahams is counselled on the implications of neural tube defects for the child and the family and offered a termination of pregnancy which she refuses. At delivery by Caesarian section the infant is born with a large closed encepholocele. Mrs Abraham’s 9 year old son also has a sacral myelomeningocoele.
List three (3) teratogens associated with an increased risk of neural tube defects (½x3 = 1½)
Anticonvulsants, diabetes, alcohol
Mrs Abraham’s healthy adult daughter has been told she is not at any greater risk than anyone else of having a child with spina bifida as she is unaffected. She was therefore told that she does not need to take more than the recommended dose of 0,4mg of folic acid/day when planning a pregnancy. Is this advice correct? Explain your answer (2½)
No – multifactorial condition suggesting significant genetic influence so the more close relatives you have with the condition, the higher your risk and with 2 siblings affected she is at a significantly higher risk and should be taking high dose folic acid at 4mg/day
Describe how neural tube defects can be detected antenatally (2)
Foetal ultrasound by an experienced scanner is the preferred method for antenatal detection of neural tube defects. Screening by measurement of alpha-foetoprotein (AFP) in maternal serum with confirmation that the elevation is foetal by measuring the level in the amniotic fluid may also be used, usually in conjunction with ultrasound.
What factors would you take into account when discussing the recurrence risk for neural tube defects with a couple? (5)
The risk to an individual pregnancy for a neural tube defect depends on the following:
- The background risk in that population (1)
- The family history - Affected mother
o Previously affected child
o Family history of close relative with NTD
o (Risk rises with increasing numbers of affected relatives) (2)
- potential teratogens exposure including drugs (particularly anticonvulsants, alcohol etc.) (2)
Explain why the AFP is elevated (2)
The open neural tube allows flow of AFP from CSF into the amniotic fluid that is then absorbed into the circulation.
State the gestational age at which the abnormality occurs (1)
By 4 weeks embryonal development (~ 6 weeks post LMP)
State whether this couple may legally terminate the pregnancy and explain your answer (1½)
Yes – TOP allowed legally for “severe malformation of the fetus” at any gestation
List six (6) factors which may influence Mr and Mrs Jacobs’ decision to terminate or not (3)
Risk perception, acceptance of burden, religion, value system, interpersonal relationship, lifestyle and educational level, emotional state
